The present study has attempted to establish a new method of non-destructive inspection method for material degradation by using martensitic transformation. Martensitic phase transformation occurs in an austenitic stainless steel SUS304 and thus resultant magnetization is induced due to severe deformation or to high applied stress. Peaks of vertical magnetic flux density B_z were measured in the plates of SUS304 stainless steel with fatigue cracks by flux gate sensor. The distance 2l between the minimum and the maximum peaks of the B_z distribution shows a linear correlation with real fatigue crack length 2a. The values of minimum and maximum peaks also have a linear relationship with the applied stress intensity factor range ΔK, a kind of a fatigue damage parameter imposed. These results imply that the measurement of the vertical magnetic flux density above a fatigue crack can estimate real crack length 2a and the amount of damage the specimens has suffered.
